Crassolabium unicum, Nguyen & Peña-Santiago, 2021

Nguyen, Thi Anh Duong & Peña-Santiago, Reyes, 2021, Description of Crassolabium unicum sp. n. (Nematoda: Dorylaimida: Qudsianematidae) from Vietnam, Zootaxa 4970 (1), pp. 189-194 : 190-192

Crassolabium unicum sp. n.

Figures 1 , 2 ; Table 1

Material examined. Twenty females from one location, in good state of preservation. Morphometrics. See Table 1 .

Description. Female: Stout (a = 17–20) nematodes of small size, 0.77–0.94 mm long. Body cylindrical, tapering towards both ends, but more so towards the anterior end as the tail is short and rounded. Upon fixation, habitus variable, often slightly curved ventrad, C-shaped, sometimes somewhat sigmoid. Cuticle three-layered, more appreciable at caudal region, 1.5–2 µm thick at anterior region, 2–3 µm in mid-body, and 3.5–6 µm on tail; outer layer thin, smooth, with constant thickness throughout the body; intermediate layer much thicker than the outer layer, specially conspicuous at tail; inner layer thinner than the intermediate one. Lateral chord 7.5–12 µm broad, occupying up to one-fourth (17–24%) of mid-body diameter. Body pores obscure. Lip region slightly angular, offset by a shallow (but perceptible) depression, 2.5–2.9 times broader than high and ca one-third (28–35%) of body diameter at neck base; lips mostly amalgamate, with somewhat protruding labial and cephalic papillae. Amphid fovea cup-like, its aperture 3–4 µm, occupying up to one-third (22–32%) of lip region diameter. Cheilostom nearly cylindrical, with relatively thick walls. Odontostyle comparatively strong, almost equal (1.0–1.2 times) the lip region diameter long, 5.2–5.8 times as long as broad, and 1.46–1.76% of total body length; aperture 5–6.5 µm long, occupying less than one-half (36–46%) of odontostyle length. Guiding ring protruded in all the specimens examined, but apparently simple, not plicate. Odontophore rod-like, 1.4–1.6 times as long as odontostyle. Pharynx entirely muscular, gradually enlarging into the basal expansion that is 5.7–6.9 times as long as wide, 2.8–3.3 times longer than body diameter at neck base and occupies ca one-half (47–52%) of neck length; gland nuclei located as follows: DO = 51–57, DN = 54–60, S 1 N obscure, S 2 N = 82–85. Nerve ring situated at 79–88 µm or 31–36% of total neck length from the anterior end. Pharyngo-intestinal junction consisting of a conoid, 8–14 x 7–10.5 µm cardia, enveloped by intestinal wall. Intestine bearing conspicuous folds at its anterior part behind its junction to pharynx. Genital system didelphic-amphidelphic, with both branches equally developed, anterior 66–140 µm or 6–15%, posterior 78–144 µm or 9–16% of total body length. Ovaries reflexed, the anterior 34–112 µm, the posterior 46–106 µm long, often reaching and surpassing the oviduct-uterus junction, with oocytes arranged first in two or more rows and then in a single row. Oviduct 24–47 µm long or 0.6–0.9 body diameters long, consisting of a distal, slender section made of prismatic cells and a poorly developed proximal pars dilatata with visible lumen inside. A marked narrowing surrounded by muscular ring (sphincter) separates oviduct and uterus. Uterus a simple tube-like structure 28–43 µm or 0.7–0.9 body diameters long. Uterine egg ovoid, 63–70 x 29–35 µm. Vagina extending inwards 16.5– 23 µm, occupying 37–52% of body diameter: pars proximalis 10–16 x 7–8.5 µm, with somewhat sigmoid walls and surrounded by poor to moderately developed circular musculature; pars refringens consisting of (in lateral view) two rectangular to trapezoidal sclerotized pieces, 1.5–3 x 2.5–4.5 µm, with a combined width of 8–11 µm; two very small sclerotized pieces are always present close to those forming part of pars refringens; pars distalis 3.5–5 µm long. Vulva apparently a wide transverse slit. Prerectum 1.4–2.4 times the anal body diameter long, often with a visible fold in its wall and a small (but distinct in most specimens) postrectal blind sac in dorsal position. Rectum 1.1–1.3 times the anal body diameter long. Tail short and rounded, hardly more straight ventrally; intermediate cuticle layer reaching the tail tip, but detached from the outer layer, thus existing two (dorsal and ventral) visible spaces (lacunae) between them, the ventral one always more developed; caudal pores two pairs, one lateral, a short distance behind the anus level, other subdorsal, at the anterior third of tail length.

Male: Unknown.

Diagnosis. The new species is characterized by its 0.77–0.94 mm long body, three-layered cuticle, lip region offset by depression and 12–13.5 µm broad, odontostyle 13.5–15 µm long with wide aperture occupying 36–46% its length, neck 235–260 µm long, pharyngeal expansion 117–131 µm long or occupying 47–52% of total neck length, intestine bearing distinct folds at its anterior part, female genital system didelphic-amphidelphic, uterus simple and 28–43 µm or 0.7–0.9 body diameters, vulva transverse (V = 45–52), prerectum bearing a blind postrectal sac, caudal region short and rounded (21–25 µm, c = 45–61, c’ = 0.6–0.8) with two (dorsal and ventral) lacunae between outer and intermediate cuticle layers, and male unknown.

Relationships. In having small size (body up to 1.0 mm long) and comparatively short odontostyle (less than 15 µm long), the new species resembles C. ettersbergense (de Man, 1885) , C. medianum ( Eroshenko, 1976) , C. parvulum ( Thorne & Swanger, 1936) and C. pumilum ( Andrássy, 1963) . It differs from all of them in several peculiar traits: three- (vs very often two-) layered cuticle, anterior region of intestine showing visible folds, presence (vs absence) of a postrectal blind sac, and the presence of lacunae between outer and intermediate cuticle layers. Besides, it can be distinguished from C. ettersbergense , a widely spread species, in its broader lip region (12–13.5 vs 8 µm), longer odontostyle (13.5–15 vs 8–11 µm), and much more anterior vulva (V = 45–52 vs V = 57–69). From C. medianum in its slightly longer odontostyle (13.5–15 vs 11–12.5 µm) and different tail morphology: short and rounded (vs conoid), absence (vs presence) of cuticle irregularities at ventral side, and lacking (vs having) a distinct hyaline terminal portion. From C. parvulum , a poorly described species, in its much wider odontostyle aperture (36–46% vs one-fifth of odontostyle length), longer pharyngeal expansion (47–52% vs two-fifths of the total neck length), and more rounded (vs convex conoid) tail. From C. pumilum in its somewhat larger general size (body length 0.77–0.94 vs 0.60–0.67 mm), longer odontostyle (13.5–15 vs 9–9.5 µm), much longer pharyngeal expansion (47–52 vs 30–34% of the total neck length), presence (vs absence) of pars refringens vaginae, and more anterior vulva (V = 45–52 vs V = 58–60).

Type locality and habitat. Northern Vietnam, Cao Bang Province, Cao Bang National Park ( GPS coordinates: 22º 36’17’’ N and 105º 52’58’’ E), in a tropical forest soil with Neohouzeaua sp. and Pteris sp. as dominant plant species.

Type material. Female holotype and eleven female paratypes deposited with nematode collection of the University of Jaén , Spain . Eight female paratypes deposited with the nematode collection of the Institute of Ecology and Biological Resources ( IEBR), Hanoi, Vietnam .

Etymology. The specific epithet is the Latin term unicum = unique, and refers to the peculiar combination of traits that characterize the new species.

Figures

FIGURE 1. Crassolabium unicum sp. n. from Vietnam (female). A: Entire. B, C: Anterior region in lateral median view. D: Anterior genital branch. E: Lip region in lateral surface view. F, G: Pharyngointestinal junction. H: Vagina. I, J: Posterior body region. K, L: Caudal region. [Scale bars: A = 100 µm; B = 10 µm; C, E, H, K, L = 5 µm; D, F, G, I, J = 20 µm.]

FIGURE 2. Crassolabium unicum sp. n. from Vietnam (female, LM).A, B: Entire. C, D:Anterior region in lateral median view. E: Anterior genital branch. F: Lip region in lateral surface view. G–I: Pharyngointestinal junction. J: Vagina. K–M: Posterior body region. N: Uterine egg. O: Posterior genital branch. P–R: Caudal region. [Scale bars: A, B = 100 µm; C = 10 µm; D, F, J, P–R = 5 µm; E, G–I, K–O = 20 µm.]